438 JAMES WATT. 
Jel ray, infinitely diluted with the solar light that falls on 
the first surface, issues from the second surface, diverging 
and with a sensible breadth, it is because the glass sepa- 
rates that which, in the white pencil, was by its nature 
unequally refrangible.” These words are nothing but a 
literal translation of the known experiment of the pris- 
matic solar spectrum. ‘This translation, however, had 
escaped an Aristotle, a Descartes, a Robert Hooke. 
Without departing from ‘the subject, let us come to 
some arguments which will lead in a still more direct line 
to the point. The theory conceived by Watt of the com- 
position of water reaches London. If it had been accord- 
ing to the ideas of those times, as simple, as self-evident 
as it appears to us now, the counsel of the Royal Society 
would not have failed to adopt it: but its strangeness 
made them doubt the correctness of Priestley’s experi- 
ments. They went so far as to laugh at it, said De Luc, 
as at the explanation of the golden tooth. 
A theory, the conception of which did not present any 
difficulty, would certainly have been despised by Caven- 
dish. But recollect with what eagerness, under the in- 
spiration of that man of genius, Blagden claimed ‘the 
priority of it against Lavoisier. 
Priestley, to whom a great part of the honour of Watt’s 
discovery belonged,—Priestley, whose affectionate sen- 
timents for the celebrated engineer cannot be doubted, 
wrote to him, under date of the 29th April, 1783,— 
“Look with surprise and indignation at the drawing of 
an apparatus, by the aid of which I have irrevocably 
undermined your beautiful hypothesis.” 
In conclusion, an hypothesis at which they laughed in 
the Royal Society ; which made Cavendish emerge from 
his habitual reserve ; which Priestley, laying all self-love 
